Argument is a situation in which two or more people disagree, often angrily.
One of them supports a subject or an idea, while the other opposes it. This leads to a disagreement between the two.

In a screenplay, two people are involved in an argument; the Hero and the Villain. They argue over a subject; the theme.

The theme of a story is the main subject or idea of the story. It is the main reason for the story.
The theme of a story is the message the story sends to its audience. This massage is contained in the topic of the theme.
The theme has a motive which can be opposed or supported. This motive is the main driver of the message.
A theme in a screenplay often has a motive that preaches goodness; although, rarely, a theme can have a motive for evil.

For the theme with a good motive;
The Villain always strives to oppose the theme. He supports the negative motive of the theme.
The Hero on his own part proposes the theme. He does not support a negative motive. All he does is to maintain the positive motive.

The Hero and the Villain are two bitter rivals. The two want something; something that is limited in supply; something that has just one source; something like a coin that has two faces; something that will make or mar a people's existence; something that will favor the Hero and not the Villain, or something that will favor the Villain and not the Hero.
The Hero and the Villain are in a grievous fight. The winner of this fight takes it all.
This fight can come in various forms. All these forms equal the argument over the theme.

At some points, the Villain may appear to be wining. At some other points, the Hero may also appear to be wining. This builds the plot.
Towards the end, the Villain may finally appear to have upheld the negative motive of the theme. But just a moment before the end, the Hero will unexpectedly outclass the Villain to uphold the positive motive of the theme.

Let's take for example, where a theme of your screenplay is:

''It pays to honor the king"

The Villain will argue thus:

''It does not pay to honor the king"

The Villain has supported the negative motive of the theme; ''It does not pay to honor the king"

But the Hero will surely support the positive motive; ''It pays to honor the king"

Application of theme debate
The debate or argumate between the Hero and the Villain can help a writer to complete a very thrilling story or screenplay.

Story structure: The argument proceedings help to sharpen the story and then bare its main structure.

Plot: The series of rise and fall of both the Villain and the Hero goes a long way in building the plot.

Conflict: The argument is the conflict. The more the argument gets heated, the more the conflict rises.

Character: The processes involved in the arguments describe the characters the more. These processes inform the audience who the main characters in the argument are. It also measures and tells the audience the amount of energy each of them is putting in to achieve their desires. It describes precisely how these two characters live their lives.

The end: The end will be well defined. At last, it's either the Villain or the Hero would win.

Procedure for theme debate
Here is how to handle the theme debate for better result

Let your theme generate a lot of argument.

Create very ambitious characters.

Let the strengths and energies of the two opponents to be almost equal.

Let the chances of both in getting their desires to be limited and tough.